The invention is related to semiconductor devices in which a lengthened optical interaction beam path is provided to enhance interaction of a probe beam and charge carriers present in a carrier region of the devices.
Recently, noninvasive optical techniques have been developed for probing integrated circuit devices. These techniques are based on the phenomenon that if semiconductor material (for example GaAs and Si) is probed by an optical probe beam having a wavelength outside the absorption band of the material, any charge carriers present in the area probed will cause a change in the phase and/or polarization of the probe beam. (See, for example, J. L. Freeman et al Appl. Phys. Lett. 47, 1083 (1985), B. H. Kolner et al, "Electro-optic Sampling in GaAs Integrated Circuits", IEEE Journal of Quantum Electronics, Vol. QE-22, 79 No. 1, January 1986 and H. K. Heinrich et al, "Noninvasive Sheet Charge Density Probe for Integrated Silicon Devices", Applied Physics Letter 48(16), pp 1066-1068, Apr. 21, 1986.) The change in the probe beam can be detected and used to determine if a charge is present, and accordingly, whether an electronic device--such as an FET--is activated or storing charge. A plurality of optical memory elements may be interconnected to form a random access memory array as described in the application of Aaron Falk entitled "Opto-Electronic Memory Device", Ser. No. 07/203,495 filed concurrently herewith and incorporated herein by reference.
In conventional semiconductor devices, the probe beam must enter the substrate of the device in a substantially perpendicular manner in order to probe the charge carrier region. The charge carrier region, however, usually consists of a long thin region parallel to the surface of the substrate. Thus, the probe beam passes through the shortest dimension of the charge carrier region limiting the interaction path length of the probe beam and the charge carriers.